Abstract: Integrated active cooling of high-power reflective or diffractive optics uses substrates manufactured from low-expansion ceramics to flow coolant between the back surface of the substrate and chambers behind but adjacent a reflective front surface, in a direction transverse to the front surface, to thereby achieve much greater average power handling than known cooling techniques.

Abstract: A variable radius mirror includes a mirror element having a deformable face with an outer surface incorporating a reflective element. The deformable face is deformable in response to a pressure applied by a pressure medium acting on an inner surface of the deformable face. A ring extends around a perimeter of the deformable face and protrudes from the inner surface of the deformable face. The mirror element further includes at least one of a plurality of steps recessed at different depths into the inner surface of the deformable face, a cooling cavity having a pair of manifolds between the outer surface and the inner surface of the deformable face, and a sidewall of the ring having a curved inner surface and a curved outer surface.

Abstract: A guidance system for a missile performs a method for guiding the missile. The guidance system includes a target detector and a window between a target and the target detector. The window including a first pane, a second pane and a channel between the first pane from the second pane. Radiation from the target passes through the window including the first pane, the second pane and the channel to be detected at the target detector. A gas is transported through the channel between the first pane and the second pane to control a temperature of the window.

Abstract: A near-eye light field display device is provided. The near-eye light field display device includes a first lens, a micro-lens array, a second lens, and a display panel. The display panel is adapted to provide an image beam. An eye-side surface of the micro-lens array is provided with a plurality of eye-side micro lenses, and a display-side surface thereof is provided with a plurality of display-side micro lenses. The eye-side micro lenses are arranged equidistantly in a first pitch. The display-side micro lenses are arranged equidistantly in a second pitch. The first pitch is different from the second pitch.

Abstract: A method of forming a ceramic matrix composite component with cooling channels includes embedding a plurality of wires into a preform structure, densifying the preform structure with embedded wires, and removing the plurality of wires to create a plurality of corresponding channels within the densified structure.

Abstract: The disclosure provides a method that includes filling a cavity in a substrate with a second material, wherein the substrate includes a first material. The method also includes using galvanic and/or chemical deposition of a third material to apply an overcoating to a first surface of the substrate in a region of the cavity. The method further includes removing the second material from the cavity. In addition, the method includes, before or after removing the second material from the cavity, applying a reflective layer to the overcoating. The disclosure also provides related optical articles and systems.

Abstract: A method of laser processing of a metallic material is described, by means of a focused laser beam having a predetermined transverse power distribution on at least one working plane of the metallic material, comprising the steps of: providing a laser beam emitting source; leading the laser beam along a beam transport optical path to a working head arranged in proximity to the material; collimating the laser beam along an optical axis of propagation incident on the material; focusing the collimated laser beam in an area of a working plane of the material; and conducting said focused laser beam along a working path on the metallic material comprising a succession of working areas, wherein the laser beam is shaped: by reflecting the collimated beam by means of a deformable controlled surface reflecting element having a plurality of independently movable reflection areas, and by controlling the arrangement of the reflection areas to establish a predetermined transverse power distribution of the beam on at leas

Abstract: A display mirror assembly for a vehicle includes a housing. An electro-optic element may be operably coupled with the housing. A circuit board may be adjacent the electro-optic element. An electrostatic fluid accelerator may be adjacent the circuit board and may be configured to move ions within the housing. An actuator device may be disposed on the housing and may be operably coupled with the electro-optic element. The actuator device may be adjustable to tilt the electro-optic element in one direction, thereby moving the electro-optic element to an off-axis position which approximately simultaneously changes an activation state of a display module. The actuator device may be also adjustable to tilt the electro-optic element in another direction, thereby moving the electro-optic element to an on-axis position which approximately simultaneously changes the activation state of the display module.

Abstract: Methods, devices, and systems for elongating a beam path of a light beam, in particular of a laser beam, are provided. An example method includes coupling the light beam into an interspace between a plurality of first reflective surfaces and a plurality of second reflective surfaces facing the first reflective surfaces, multiply reflecting the light beam between the first reflective surfaces and the second reflective surfaces to elongate the beam path of the light beam, and coupling out the light beam from the interspace. The light beam undergoes the steps of coupling in, repeated reflecting and coupling out at least a first time with a first pass and a second time with a second pass, and the light beam traverses a different beam path in the interspace during the first pass in comparison with during the second pass.

Abstract: A projection apparatus includes a light source, a light reflective member, a light valve, and a light beam adjusting member. The light source is configured to provide an illumination beam. The light reflective member is configured to reflect the illumination beam. The light valve is configured to convert the illumination beam reflected by the light reflective member into an image beam. The light beam adjusting member is optically coupled between the light source and the light reflective member and includes a collimating lens module. The collimating lens module has a light entering surface and a light leaving surface respectively at opposite sides thereof. The light entering surface and the light leaving surface respectively have a first optical axis and a second optical axis extending along different directions.

Abstract: An apparatus for producing a three-dimensional work piece comprises a process chamber accommodating a carrier for receiving a raw material powder and an irradiation device for selectively irradiating electromagnetic or particle radiation onto the raw material powder applied onto the carrier in order to produce the work piece from said raw material powder by an additive layer construction method, the irradiation device comprising at least one radiation source and at least one optical unit with a plurality of optical elements. A heat transfer arrangement is configured to transfer heat generated by a heat source to the at least one optical unit of the irradiation device. The apparatus further comprises a control unit configured to control the heat transfer arrangement so as to adjust a temperature of the at least one optical unit of the irradiation device.

Abstract: In some embodiments, a catadioptric optical system (CDOS) including a centrally obscured reflective telescope is disclosed, which includes: a telescope compartment defining a telescope space therein, a primary reflector including a central opening and a secondary reflector. The reflectors are located in the telescope compartment. The CDOS also includes a mechanism for reducing temperature gradient in the telescope space. The mechanism includes an air duct including a first opening and a second opening; a hollow enclosure including side openings and one or more airflow generation devices. The mechanism is configured for forming an air passageway between the airflow generation device and the inner telescope space via the air duct and hollow enclosure located therebetween, for reducing internal air temperature gradient in the telescope space.

Abstract: The disclosure provides a method that includes filling a cavity in a substrate with a second material, wherein the substrate includes a first material. The method also includes using galvanic and/or chemical deposition of a third material to apply an overcoating to a first surface of the substrate in a region of the cavity. The method further includes removing the second material from the cavity. In addition, the method includes, before or after removing the second material from the cavity, applying a reflective layer to the overcoating. The disclosure also provides related optical articles and systems.

Abstract: An optical assembly includes: an optical element, which is transmissive or reflective to radiation at a used wavelength and has an optically used region; and a thermally conductive component, which is arranged outside the optically used region of the optical element. The thermally conductive component can include a material having a thermal conductivity of more than 500 W m?1 K?1. Additionally or alternatively, the product of the thickness of the thermally conductive component in millimeters and the thermal conductivity of the material of the thermally conductive component is at least 1 W mm m?1 K?1.

Abstract: The disclosure provides a method that includes filling a cavity in a substrate with a second material, wherein the substrate includes a first material. The method also includes using galvanic and/or chemical deposition of a third material to apply an overcoating to a first surface of the substrate in a region of the cavity. The method further includes removing the second material from the cavity. In addition, the method includes, before or after removing the second material from the cavity, applying a reflective layer to the overcoating. The disclosure also provides related optical articles and systems.

Abstract: An illumination optical unit for EUV projection lithography illuminates an object field with illumination light. The illumination optical unit has a first facet mirror including a plurality of first facets on a first mirror carrier. Disposed downstream of the first facet mirror is a second facet mirror including a plurality of second facets arranged on a second mirror carrier around a facet arrangement center. Partial beams of the illumination light are guided superposed on one another into the object field, respectively via illumination channels which have one of the first facets and one of the second facets. Second maximum angle facets are arranged at the edge of the second mirror carrier. The second maximum angle facets predetermine maximum illumination angles of the illumination light which deviate maximally from a chief ray incidence on the object field.

Abstract: The present disclosure generally pertains to lightweight adaptive metal cooled mirrors and methods of producing the same. The metal mirror surface is integrated with and supported by metal channels which are physically incorporated into the mirror surface through an additive manufacturing process. These channels are nominally conformal with the desired mirror surface shape. A liquid or gaseous coolant may be directed through some or all of the channels to cool the mirror surface. The mirrors are produced through an additive manufacturing process which allows for the creation of a unitary optical mirror containing finely spaced channels.

Abstract: An apparatus for generating extreme ultraviolet light used with a laser apparatus and connected to an external device so as to supply the extreme ultraviolet light thereto includes a chamber provided with at least one inlet through which a laser beam is introduced into the chamber; a target supply unit provided on the chamber configured to supply a target material to a predetermined region inside the chamber; a discharge pump connected to the chamber; at least one optical element provided inside the chamber; an etching gas introduction unit provided on the chamber through which an etching gas passes; and at least one temperature control mechanism for controlling a temperature of the at least one optical element.

Abstract: A reflector (2) comprising a plate (4) supported by a substrate (8), wherein the plate has a reflective surface (5) and is secured to the substrate by adhesive free bonding, and wherein a cooling channel array (10) is provided in the reflector. The channels (16) of the cooling channel array may be formed from open channels in a surface of the substrate, the open channels being closed by the plate to create the channels.

Abstract: An apparatus for forming an optical pattern includes a vacuum chamber, a mount on which a substrate to be prepared using a mask is to be supported, a diffusion unit adjacent the mask, spaced apart from the mask by a preset interval, and facing the mask, the diffusion unit to diffuse light incident thereon as uniform surface light and transmit the uniform surface light to the mask, and a light source unit spaced in a lateral direction from the diffusion unit, the light source unit to generate light to be incident on the diffusion unit.

Abstract: An optical system of a microlithographic projection exposure apparatus designed for an operating wavelength of at least 150 nm. In one disclosed aspect, the optical system includes an element (11, 21) producing an angular distribution for light incident during the operation of the optical system and a fly's eye condenser (200, 400, 500) which includes two arrangements (210, 220, 410, 420, 510, 520) following one another in the light propagation direction and made of beam-deflecting optical elements (211-213, 221-223, 411-413, 421-423, 511-513, 521-523), which produce a multiplicity of optical channels. No optical element with refractive power is arranged in the beam path between the element (11, 21) producing an angular distribution and the fly's eye condenser (200, 400, 500).

Abstract: The invention relates to an optical element for a projection exposure apparatus for semiconductor lithography comprising an optically active surface and at least one cooling component for cooling the optical element, wherein the cooling component is connected to at least two separate cooling circuits and embodied in such a way that the optically active surface can be cooled to a greater extent in at least one partial region than in a further partial region. The invention furthermore relates to a projection exposure apparatus comprising an optical element according to the invention.

Abstract: Focus of a laser optical system can be corrected using a variable radius mirror having a focusing cavity and a separate cooling cavity. Pressure of a focusing material at a sufficiently low mass flow in the focusing cavity deforms a reflective surface mounted to the focusing cavity, changing its radius. Cooling material provided to the cooling cavity cools the variable radius mirror. A laser beam is reflected by the deformed reflecting surface to focusing optics, focusing the reflected laser beam on an EUV-emitting target, and minimizing a laser focus error by one or more of: maximizing a measured EUV power or minimizing a measured laser beam divergence. Providing focusing material at a deformation pressure and at a sufficiently low mass flow, and providing a separate cooling cavity, avoids perturbations in the reflective surface which would otherwise affect laser beam focus.

Abstract: A deterioration of the collector performance in an extreme ultraviolet light source device due to a heat deformation of the collector mirror assembly is to be prevented. The collector mirror assembly used in the extreme ultraviolet light source device comprises a plurality of reflective shells 21 with different diameters which are shaped as ellipsoids of revolution or hyperboloids of revolution, wherein the reflective shells 21 are arranged in a nested shape and the ends thereof are held by a holding structure 22. A cooling channel, through which a cooling medium flows is mounted at the reflective shell 21 in the axial direction of the reflective shell on the face being the back side of the reflective surface. This cooling channel acts as a reinforcement material and is able to suppress a heat deformation of the reflective shell 21.

Abstract: A method for cooling an optical element for EUV applications is disclosed. Heat is transferred from the optical element to a heat sink, and, via a first feed line, a first cooling medium is introduced into a cooling channel in the heat sink, in such a way that the first cooling medium effects laminar flow through the cooling channel and in the process absorbs heat from the heat sink. After flowing through the cooling channel, the first cooling medium is discharged into a discharge line leading away from the optical element. A second cooling medium is introduced into the discharge line via a second feed line, and the first cooling medium and the second cooling medium, downstream of the second feed line at a location that is further away from the optical element than the cooling channel, are subjected to a force field introduced into the discharge line externally.

Abstract: A curvature variable mirror includes a mirror base material that is configured such that the curvature is variable and that reflects laser light on the mirror reflective surface side, wherein the mirror base material is formed by using spring-material copper alloy, and the spring-material copper alloy is constituted by using any of phosphor bronze, copper-nickel-zinc alloy, chromium copper, zirconium copper, titanium copper alloy, copper-nickel alloy, and alloy obtained by adding at least one of Ni (nickel), Sn (tin), Si (silicone), Mg (magnesium), Zn (zinc), Mn (manganese), Pb (lead), Fe (iron), and Al (aluminum) to copper.

Abstract: The disclosure provides a cooler for use in a plasma generation chamber of a radiation source for an extreme ultraviolet wavelength range. The cooler has a heat sink which is at least partially manufactured of a substrate material having a thermal conductivity of greater than 50 W/mK. A coolant duct is formed in the substrate material, and the coolant duct is configured to have a coolant flow therethrough. The cooler also includes a connection piece made of a metal or a metal alloy for connecting a coolant line to the coolant duct. The cooler further includes a connecting element for connecting the connection piece to the heat sink so that, when the connection piece is connected to the heat sink, a continuous line is formed by the coolant duct and the coolant line.

Abstract: A mirror assembly (32) for directing a beam (28) includes a base (450), and an optical element (454) that includes (i) a mirror (460), (ii) a stage (462) that retains the mirror (460), (iii) a mover assembly (464) that moves the stage (462) and the mirror (460) relative to the base (450), and (v) a thermally conductive medium (466) that is positioned between the stage (462) and the base (450) to transfer heat between the stage (462) and the base (450). The thermally conductive medium (466) has a thermal conductivity that is greater than the thermal conductivity of air. The thermally conductive medium (466) can include an ionic fluid or a liquid metal.

Abstract: A device serves for controlling temperature of an optical element provided in vacuum atmosphere. The device has a cooling apparatus having a radiational cooling part, arranged apart from the optical element, for cooling the optical element by radiation heat transfer. A controller serves for controlling temperature of the radiational cooling part. Further, the device comprises a heating part for heating the optical element. The heating part is connected to the controller for controlling the temperature of the heating part. The resulting device for controlling temperature in particular can be used with an optical element in a EUV microlithography tool leading to a stable performance of its optics.

Abstract: A mirror with a mirror carrier, as well as related apparatuses, systems and methods are disclosed. The mirror carrier can be embodied as cooling device with at least one cooling channel. Tube connections can be provided to connecting the at least one cooling channel to an inlet and an outlet of coolant. Sealing elements for a gas-tight and liquid-tight seals can be arranged between the tube connections and the mirror carrier. The field of application of the mirror can be, for example, an illumination device of a projection exposure apparatus.

Abstract: An optical system including an optical element, a positioning mechanism configured to position the optical element into an operational position, and a temperature control mechanism configured to intermittently control the temperature of the optical element between operations. By alternatively positioning the optical element between an operational position and a position in thermal contact with the temperature control mechanism, the two mechanisms for positioning and controlling the temperature of the optical element are de-coupled from one another. As a result, the mechanism for each may be optimized In non-exclusive embodiments, the temperature control mechanism may be used to control the temperature of an individual optical element or a plurality of optical elements, such as for example, a fly's eye mirror used in an illumination unit of an EUV lithography tool.

Abstract: A fogless shower mirror includes a mirror assembly having an elongated hollow body which has a thin, rectangular-shaped mirror frame section on which is mounted a mirror plate, and an upper rearwardly curved water supply conduit section. A rectangular slab-shaped reservoir within the mirror frame communicates at the upper end thereof with a bore through the water supply conduit, which has at an outer end thereof a vertically disposed water fill aperture. The reservoir and water supply conduit are filled with warm water, and the mirror assembly is releasably attached to a mirror support stand attached to a shower enclosure wall. The mirror plate is heated by the warm water in the reservoir to thus resist fogging caused by condensation of water vapor, Water cooled by warming the mirror plate trickles from a small drain hole in the reservoir and is replenished with warm water from the water supply conduit.

Abstract: Evaporate thermal management systems for and methods of grazing incidence collectors (GICs) for extreme ultraviolet (EUV) lithography include a GIC shell interfaced with a jacket to form a structure having a leading end and that defines a chamber. The chamber operably supports at least one wicking layer. A conduit connects the wicking layer to a condenser system that support cooling fluid in a reservoir. When heat is applied to the leading end, the cooling fluid is drawn into the chamber from the condenser unit via capillary action in the wicking layer and an optional gravity assist, while vapor is drawn in the opposite direction from the chamber to the condenser unit. Heat is removed from the condensed vapor at the condenser unit, thereby cooling the GIC mirror shell.

Abstract: An illumination optical unit for projection lithography has a first polarization mirror device to reflect and polarize of illumination light. A second mirror device, which is disposed downstream of the polarization mirror device reflects an illumination light beam. At least one drive device is operatively connected to at least one of the two mirror devices. The two mirror devices are displaceable relative to one another via the drive device between a first relative position, which leads to a first beam geometry of the illumination light beam after reflection at the second mirror device, and a second relative position, which leads to a second beam geometry of the illumination light beam after reflection at the second mirror device, which is different from the first beam geometry. This results in a flexible predefinition of different illumination geometries, in particular of different illumination geometries with rotationally symmetrical illumination.

Abstract: The invention relates to an optical element for a projection exposure apparatus for semiconductor lithography comprising an optically active surface and at least one cooling component for cooling the optical element, wherein the cooling component is connected to at least two separate cooling circuits and embodied in such a way that the optically active surface can be cooled to a greater extent in at least one partial region than in a further partial region. The invention furthermore relates to a projection exposure apparatus comprising an optical element according to the invention.

Abstract: A fly's eye mirror including first and second complementary M×N arrays, each including a plurality of faceted reflective surfaces arranged along both the first and the second axes. When assembled, the two complementary arrays are integrated together and mounted onto a common base plate. With the increased lineal length of each array along both axes, the faceted reflective surfaces of each array are in rotational or tilt alignment with a base plate along both axes.

Abstract: A device serves for controlling temperature of an optical element provided in vacuum atmosphere. The device has a cooling apparatus having a radiational cooling part, arranged apart from the optical element, for cooling the optical element by radiation heat transfer. A controller serves for controlling temperature of the radiational cooling part. Further, the device comprises a heating part for heating the optical element. The heating part is connected to the controller for controlling the temperature of the heating part. The resulting device for controlling temperature in particular can be used with an optical element in a EUV microlithography tool leading to a stable performance of its optics.

Abstract: A method for processing workpieces includes performing a laser processing operation in which a laser beam is directed at a first mirror face and at a second mirror face of a redirecting mirror. The second mirror face is at least partially surrounded by the first mirror face. During the laser processing operation, the second mirror face performs a pendulum movement relative to the first mirror face.

Abstract: The invention relates to an adaptive mirror based on a ceramic substrate having a corresponding reflector and piezoelectric actuators, a cooling device being integrated in the substrate. The invention likewise relates to a method for the production of such mirrors. The mirrors according to the invention are used for the modulation or deformation of a laser wavefront of high power.

Abstract: A device serves for controlling temperature of an optical element provided in vacuum atmosphere. The device has a cooling apparatus having a radiational cooling part, arranged apart from the optical element, for cooling the optical element by radiation heat transfer. A controller serves for controlling temperature of the radiational cooling part. Further, the device comprises a heating part for heating the optical element. The heating part is connected to the controller for controlling the temperature of the heating part. The resulting device for controlling temperature in particular can be used with an optical element in a EUV microlithography tool leading to a stable performance of its optics.

Abstract: A mirror module is provided with comprising a reflective element, a supporting base element attached to the reflective element, and a heat exchange element for transferring heat to and/or from the mirror module. The mirror module, more in particular the reflective element, is stabilized against possible deformation due to a thermal load. The stabilized mirror module comprises heat pumps, for example Peltier elements, for transferring heat between the heat exchange element on one hand and the reflective element and the base element on the other hand, more in particular for cooling the reflective element. A method is provided to stabilize a mirror module wherein a heat flow is measured to stabilise the shape of a reflective element.

Abstract: A reflective optical element for use in an EUV system is disclosed. The reflective optical element includes a base body, which is produced at least partly from a substrate material. At least one cooling channel through which a cooling medium can flow is arranged in the base body. A material having a thermal conductivity of greater than 50 W/mK is provided as substrate material. The reflective optical element also includes a polishing layer, which is applied on the substrate material. The polishing layer includes an amorphous material which can be processed via polishing.

Abstract: A method for cooling a structure includes flowing a saturated refrigerant through one or more passageways in the structure while maintaining the refrigerant at a substantially constant pressure. The method also includes evaporating at least a portion of the refrigerant at a substantially constant temperature throughout the passageways in the structure.

Abstract: A deterioration of the collector performance in an extreme ultraviolet light source device due to a heat deformation of the collector mirror assembly is to be prevented. The collector mirror assembly used in the extreme ultraviolet light source device comprises a plurality of reflective shells 21 with different diameters which are shaped as ellipsoids of revolution or hyperboloids of revolution, wherein the reflective shells 21 are arranged in a nested shape and the ends thereof are held by a holding structure 22. A cooling channel, through which a cooling medium flows is mounted at the reflective shell 21 in the axial direction of the reflective shell on the face being the back side of the reflective surface. This cooling channel acts as a reinforcement material and is able to suppress a heat deformation of the reflective shell 21.

Abstract: A device serves for controlling temperature of an optical element provided in vacuum atmosphere. The device has a cooling apparatus having a radiational cooling part, arranged apart from the optical element, for cooling the optical element by radiation heat transfer. A controller serves for controlling temperature of the radiational cooling part. Further, the device comprises a heating part for heating the optical element. The heating part is connected to the controller for controlling the temperature of the heating part. The resulting device for controlling temperature in particular can be used with an optical element in a EUV microlithography tool leading to a stable performance of its optics.

Abstract: In a method for producing a three-dimensionally shaped object, (i) a solidified layer is formed by irradiating a light beam on a specified portion of a powder layer to sinter or melt the specified portion. Further, (ii) another solidified layer is formed by placing a new powder layer on the solidified layer obtained in step (i), and irradiating the light beam on a specified portion of the new powder layer to sinter or melt the specified portion of the new powder layer. The steps (i) and (ii) are repeated to produce a three-dimensionally shaped object. In the method, a gas is supplied to a mirror used in scanning the light beam.

Abstract: Systems, assemblies and methods for thermally managing a grazing incidence collector (GIC) for EUV lithography applications are disclosed. The GIC thermal management assembly includes a GIC mirror shell interfaced with a jacket to form a sealed chamber. An open cell, heat transfer (OCHT) material is disposed within the metal chamber and is thermally and mechanically bonded with the GIC mirror shell and jacket. A coolant is flowed in an azimuthally symmetric fashion through the OCHT material between input and output plenums to effectuate cooling when the GIC thermal management assembly is used in a GIC mirror system configured to receive and form collected EUV radiation from an EUV radiation source.

Abstract: Methods and apparatus for cooling mirrors in an extreme ultraviolet (EUV) lithography system using a liquid metal interface are described. According to one aspect of the present invention, an apparatus which may be used in an EUV lithography system includes a heat exchanger, a mirror assembly, and a first liquid metal interface. The heat exchanger including at least a first surface. The minor assembly includes a first mirror block having a first mirrored surface, as well as at least a first well. Finally, the first liquid metal interface includes liquid metal which is contained in the first well. The first surface is in contact with the liquid metal such that heat may be transferred form the first minor block to the heat exchanger.

Abstract: A device serves for controlling temperature of an optical element provided in vacuum atmosphere. The device has a cooling apparatus having a radiational cooling part, arranged apart from the optical element, for cooling the optical element by radiation heat transfer. A controller serves for controlling temperature of the radiational cooling part. Further, the device comprises a heating part for heating the optical element. The heating part is connected to the controller for controlling the temperature of the heating part. The resulting device for controlling temperature in particular can be used with an optical element in a EUV microlithography tool leading to a stable performance of its optics.

Abstract: An optical assembly has at least one mirror with a mirror body. The latter is carried by a support body, which has a first support body portion and a second support body portion. An at least thermally separating region is arranged between the two support body portions. At least one surface portion of at least one of the support body portions or of a body thermally coupled thereto is modified in such a way that a thermal emission coefficient ?m of the modified surface portion differs from a thermal emission coefficient ?u of the unmodified surface portion by at least 10%. The result is an optical assembly, in which an improved thermal stability is achieved by the predetermining of the thermal emission coefficients.